You don't coordinate any of this — I do. Before your wedding, I connect with your DJ by email so the timeline, cues, and transition points are agreed before anyone sets up — you're copied only if you want to be.
Sound is flexible too. Typically I perform on my own professional sound system for the ceremony and cocktail hour, and at some venues the DJ's system already covers those spaces — in that case I can simply play through theirs. Either way, it's decided by email in advance, never figured out on the day. And if you want your vows heard clearly, wireless lapel microphones for your officiant and vows are available as an add-on.
On the day itself, the transition is simple: my set ends as cocktail hour winds down, and your DJ opens the reception room — no gap, no silence, no one on a microphone saying “one moment please.”